The present invention relates to a soldering or bonding apparatus, and more particularly to a vapor reflow type soldering apparatus that is suitable for soldering or bonding works of printed circuit boards or articles in which various electronic parts are arranged at a high density.
There are copending U.S. application Ser. Nos. 943,749 and 944,572 filed in the name of H. Mishina et al. on Dec. 19, 1986 and Dec. 22, 1986, respectively, and both relating to the vapor reflow type soldering apparatus.
Recently, there have been remarkably developed a high density arrangement of electronic parts in printed circuit boards, and particularly a high density arrangement of electronic parts such as so-called flat packaged I.C. each having two-dimensional electrode terminals extending in four directions, chip arts of resistors, capacitors and the like. A soldering or brazing work to attaching electronic parts such as I.C. and chips to a printed circuit board is performed in a final step of the manufacture line. For this reason, the performance of the electronic parts largely depends upon a quality of the soldering work. Thus, the soldering technique tends to be regarded as the most important and significant technique among various works in the manufacture line. Recently, a vapor reflow type soldering apparatus has been proposed which employs a vapor having a large specific weight relative to that of air as thermal medium and heats material to be processed by utilizing its condensing latent heat, in view of needs to enhance a uniformity of temperature distribution within a soldering work furnace and to avoid an undesirable excessive heating of the electronic parts.
A basic structure in which thermal medium vapor is utilized for processing is disclosed in U.S. Pat. No. 4,389,797 to Donald J. Spigarelli et al. Also, in Japanese Patent Unexamined Publication No. 106502/1980, there is shown a soldering apparatus provided with a vapor reservoir that is so called vapor reflow tank. In the latter apparatus, a solder is heated and molten by passing a printed circuit board carrying thereon electronic parts through a saturated vapor of the thermal medium within the vapor reservoir, thus performing the soldering work of the electronic parts onto the printed circuit board.
In such a vapor reflow type soldering apparatus, after the parts to be processed have been brought into contact with the thermal medium vapor, the thermal medium vapor is partly condensed to drop down, or in the case where a cooler is disposed in the line, the thermal medium is cooled by the cooler to be liquefied and returned back to the vapor reservoir. Also, the vapor discharged to the path for the parts to be processed is collected by collecting means provided along the path, and is cooled and liquefied in the same manner. In this case, the thermal medium that has passed through the collecting means has a considerably low temperature in comparison with that of the thermal medium within the vapor reservoir, to temporarily decrease the temperature of the medium within the vapor reservoir and to reduce the amount of the generated vapor. This would adversely affect the work efficiency. Also, a fluoric inactive organic agent or the like is used as the thermal medium, and its viscosity at room temperature is ten to fifteen times as high as that of water. For this reason, the fluid resistance of the thermal medium is large, and it takes a long time to return it back to the vapor reservoir. It is therefore necessary to keep a sufficient liquid level of the expensive thermal medium by storing an excess of the thermal medium.
There are the same tendencies also in the case where the thermal medium is replenished from a supply tank or the like, corresponding to the reduction during the process.